This invention refers to a multiple rotary control valve for controlling a sequence of steps requiring the intake and exhaust of different fluids in the same process. More particularly, the present invention refers to a multiple rotary valve of the "pinch" type for use in conjunction with a steam sterilizing unit in which the various fluids intervening in the sterilization process are channeled by flexible conduits made of elastic, collapsible material, and compressed or released in the proper sequence by a camming rotor.
Sterilizing units or autoclaves are complex apparatus, the operation of which require precise controls. Consequently, these apparatus are costly and not easily affordable by small biochemical laboratories or dental and medical offices.
The necessity to avoid infection risks to which doctors, nurses, technicians and patients are increasingly exposed, makes it desirable to have a sterilizing apparatus which is inexpensive, efficient and easy to operate. One of the problems of such apparatus is the exacting requirements of the sterilization cycle and the necessity of sequentially controlling a series of steps comprising the admission, heating and vaporization of water, purging of steam, venting of the sterilization chamber, intake and exhaust of cooling water, etc. This series of steps must be controlled by a multiple valve centralizing the command of all process steps. These valves are generally combined, multi-way valves, or tandem-connected valves with a single actuator.
The valves used in the control of sterilization equipment are precision devices which are costly to manufacture and difficult to connect to the fluid circuits of the equipment.
The main object of the present invention is to provide a multiple rotary valve of the "pinch" type for controlling the sequential admission and/or exhausting of the fluids intervening in a steam sterilization process, which valve is inexpensive and reliable, and which valve permits reducing significantly the cost of sterilization units, rendering them affordable to doctors' offices, laboratories and institutions which normally do not use these apparatus.
Another object of the invention is to provide a multiple pinch valve for controlling a sterilizing apparatus, which is easy to assemble and disassemble, and which permits the quick replacement of the flexible conduits.
A further object of the invention is to provide a pinch valve which could be used in conjunction with conduits of substantial diameter.
An additional object of the invention is to provide a sterilizing apparatus incorporating such valve, which is simple to operate by unskilled personnel.
While "pinch" valves for controlling the flow of fluids through flexible conduits are well known, they have not been used under severe or critical conditions or where reliability and precise operation are essential. This is basically due to the fact that flexible tubes, when subject continuously to abrasive contact with clamps, cams or other pinch devices, and to high pressures and temperatures, such as those typical in sterilizing processes, have a short life span and require frequent replacement.
Therefore, the use of "pinch" valves has been limited to light duty functions such as the control of flow in devices for the administration of therapeutical fluids, laboratory apparatus handling chemical reagents, or non-critical uses such as watering apparatus.
Examples of known pinch valves are U.S. Pat. No. 3,960,149 (Bujan) which discloses a parenteral administration unit, in which a flexible tube leading from a fluid container to a hypodermic needle is gradually pinched by a wedge-like rack meshing with a toothed rotor.
Another example is U.S. Pat. No. 3,918,490 (Goda) which discloses a fluid switching apparatus wherein two sets of flexible tubes are simultaneously pinched between an elongate cam and respective backing rods to inter-connect their outlet ends.
U.S. Pat. No. 4,786,028 (Hammond) discloses a control valve comprising a rotatable cam which acts on a tube-pinching piston. A similar arrangement is shown in U.S. Pat. No. 4,694,861 (Goodale et al).
U.S. Pat. No. 4,524,944 (Sussman) discloses a plant watering device in which a rotary cam compresses, or releases, a flexible tube leading from a source of water to a dispensing nozzle. The angular position of the cam is adjusted by a rotatable knob.
U.S. Pat. No. 4,282,902 (Haynes) discloses a valve apparatus for laboratory use comprising a plurality of rotatable cams mounted on a common shaft. Each cam sequentially engages a pair of opposite levers which, in turn, pinch or release, as necessary, respective flexible tubes against backing rods.
The valves of Bujan, Goda, Sussman, are obviously unsuitable for use in conjunction with a sterilizing apparatus. Goodale's valve is very complex and expensive to manufacture. In Haynes' valve the force of the cam acts on an intermediate portion of each pinching lever, and consequently, the pinching force applied by the end of the lever on the respective tube is only a fraction of the cam force. Such force could only pinch a tube of very small diameter, such as the 1/8" tube mentioned in Haynes' specification. Besides, the diameter of the backing rod is similar to that of the tube, and this might result in a stress concentration which might cause the early failure of the tube if used in the temperature and pressure conditions prevailing in steam sterilization processes. Finally, in the Haynes valve, the flexible tubes are not positively located relative to the pinching levers, and the tubes could be easily dislodged rendering the levers inoperative.